1. Field of the Invention
This invention relates generally to heavy duty gear boxes of the type found in the drive trains of rolling mills, where clutches are employed to alternatively engage and disengage gears from their respective support shafts, and is concerned in particular with the bearing assemblies for mounting the gears on the shafts.
2. Description of the Prior Art
In arrangements of the type referred to above, when the gears are disengaged, they are free to rotate or “free wheel” with respect to their support shafts. However, when in the engaged mode, the gears are fixed with respect to their support shafts and are subjected to axial loading incidental to the driving forces being delivered to or received from other gears.
In the past, roller thrust bearings have been employed to mount the gears on their respective support shafts. The roller thrust bearings are ideally suited for supporting the gears when they are disengaged and free wheeling. It has now been determined, however, that when the gears are fixed with respect to their support shafts in the engaged mode, and the bearings are thus in a static condition, the axial loading on the gears causes the roller elements and races of the bearings to undergo accelerated localized wear in the regions where they are in frictional contact with one another. This localized wear eventually creates clearances which exceed acceptable tolerances, causing vibrations and necessitating a shut down of the equipment and replacement of the prematurely worn bearings.